There are many types of systems that process, transport, store, or utilize a pressurized fluid. The pressurized fluid may be a liquid, gas, or a mixture of a liquid and gas. The pressurized fluid may also include solid components. For example, a system may transport a pressurized gas that includes solid particulates. As another example, a system may transport solid components in a pressurized-fluid environment. To ensure the safety of these types of pressurized systems, each such system typically includes a safety device designed to prevent (or at least provide an alarm indication during) the over-pressurization of the system. In an emergency situation, the pressure of the fluid acts on the safety device to create an opening to release fluid from the system. Outside of creating an opening, the safety device may simply provide an alert warning, indicating that a dangerous over-pressure situation is occurring or may be about to occur. In devices that actually rupture, or otherwise open, venting fluid to the environment or a safety reservoir through the opening reduces the pressure in the system and prevents another portion of the system from failing due to the high pressure of the fluid.
A rupture disk is one commonly used example of a safety device. A rupture disk can be attached to a pressurized system to expose a certain portion of the rupture disk to the pressurized fluid in the system. A portion of the rupture disk exposed to the fluid is configured to rupture or tear when the fluid reaches a predetermined pressure. The tearing or rupture of the disk creates an opening through which the pressurized fluid flows to reduce the pressure in the system. A rupture disk may include a scored line of weakness designed to ensure opening at a particular location, in response to a particular pressure, and in a particular “burst pattern.” Typically, the scored line is provided by way of a laser, mechanical displacement or thinning, or chemical etching process that involves removing material from a portion of the disk. A line of weakness also may be created through a partial shearing process, as described in co-owned U.S. Pat. No. 5,934,308, the entire contents of which are hereby incorporated by reference as if set forth herein.
In the field of “reverse-buckling” rupture disk pressure relief devices, a concave/convex-shaped structure has been used as a means of providing a reliable and reproducible pressure responsive device. Known reverse-buckling devices are designed such that when the convex side of the structure is exposed to a predetermined overpressure force, the structure buckles and inverts, causing the convex side to collapse into a concave shape. The rupture disk may be designed not only to invert, but also to open by means of a line of weakness.
One type of concave/convex shaped reverse-buckling rupture disk is a frustum-shaped rupture disk. Examples of such a frustum-shaped reverse-buckling rupture disk are illustrated in FIG. 1A (PRIOR ART) and disclosed in commonly owned U.S. Pat. No. 4,576,303, and U.S. patent Ser. No. 12/149,691 (published as U.S. Pub. No. 2008/0289945 A1), the entire contents of each of which are hereby incorporated by reference. As disclosed in U.S. Pat. No. 4,576,303, and illustrated in FIG. 1A (PRIOR ART) and FIG. 1B (PRIOR ART), a known frustum-shaped reverse-buckling rupture disk 100 may include a flange portion 110, a frustum portion 130 in the shape of a truncated cone, and a central truncated portion 120. In use, the flange portion 110 may be clamped or otherwise attached to a pressurized system, with the frustum 130 and central 120 portions exposed to system pressure.
As shown in FIG. 1B (PRIOR ART), a known frustum-shaped buckling rupture disk also may include a scored line of weakness 135 in the transition between the central truncated portion 120 and the angled frustum portion 130 of the disk. Typically, the scored line is provided by way of a laser, mechanical displacement or thinning, or chemical etching process that involves removing material from the central truncated section of the frustum portion of the disk or etching a line of weakness of the desired shape.
In use, the convex face of the frustum portion of disk 100 is exposed to a pressure in a pressurized system. The angled frustum is the main control factor in determining the pressure or force load under which the frustum-shaped reverse-buckling disk will reverse and invert. This reversal is the initial factor leading to the disk 100 rupturing or opening along a line of weakness 135.
A frustum-shaped disk including the traditionally scored line of weakness of FIG. 1B may suffer from a number of drawbacks. Material displacement may undesirably deform the scored disk. Material displacement may lack precision, resulting in slight irregularities in the thickness of the remaining material. Such irregularities may include relatively thin portions in the line of weakness, which may prematurely tear (possibly creating a hole) during shipping, installation, or operation. Such irregularities also may include relatively thick portions, which may resist tearing beyond the pressure at which the disk is otherwise designed to rupture. Material displacement also may leave a “fold-over” or ridge of excess material at the edge of the line of weakness. Such excess material may visually mask imperfections in the line of weakness. Such excess material also may undesirably alter the pressure at which the line of weakness is intended to tear. A traditionally scored line may end abruptly, creating a corner at which the effects of pressure may be undesirably concentrated.
In the configuration illustrated in FIG. 1B, the line of weakness 135 is placed into tension when the central portion 120 is exposed to a pressurized system. Such a configuration may be suitable for a constant positive-pressure system (e.g., in a breathable air application). However, if system pressure fluctuates between negative and positive pressure, the line of weakness 135 may fatigue. Such fatigue may require the operating ratio of a rupture disk 100 to be much below the intended burst pressure. Operating ratio is the ratio between a peak applied pressure (Pmax) during normal operation and a designed burst pressure (Pburst) of a rupture disk (i.e., Pmax/Pburst). In a known frustum-shaped rupture disk 100, an operating ratio of at most eighty-five percent (85%) can be expected.
Also in the configuration illustrated in FIG. 1B, the line of weakness 135 is sensitive to the shape of the central portion 120. For example, shaping the central portion 120 into a domed shape (either during manufacture or use) can stretch and weaken the material at the line of weakness 135. As a result, the line of weakness 135 may tear or develop a pin hole leak at a lower pressure than the desired burst pressure.
There is a need for a pressure response structure that overcomes one or more of the deficiencies above and/or other deficiencies in the art, and/or provides additional benefits.